Various pump mechanisms for moving or compressing air in a vehicle are well known. A common example of such mechanisms is a piston compressor for generating compressed air for a variety of devices in the motor vehicle. These compressors typically include a drive shaft, a cylinder block surrounding the drive shaft, which cylinder block has a plurality of cylinder bores or channels formed therein, a swash plate mounted on the drive shaft, and a plurality of pistons coupled to the swash plate and slidably disposed in the cylinder bores. These pistons are successively reciprocated in the cylinder channels as the drive shaft rotates so that a suction stroke and a discharge stroke are alternately executed in each of the cylinder channels. One such device is disclosed in U.S. Pat. No. 6,439,857, which is assigned to the assignee of the present application and which is incorporated herein by reference, which describes a swash plate compressor employing pistons disposed in channels of a stationary cylinder block, wherein a non-rotatable swash plate pivots in accordance with the thrust exerted by an actuator.
In these types of compressors, a space in the cylinder channel above the pistons is in fluid communication with the air system of the vehicle via inlet and outlet ports. Accordingly, the air pressure in the space in the channels corresponds to air pressure in the air system, thereby ensuring a state of pressure equilibrium for the compressor.
In order to alternately provide fluid communication and provide a seal between the inlet and outlet ports and the cylinder channels, the compressor is provided with a plurality of one-way check valves which prevent the back-feeding of the air. These valves are often of the reed variety, such as those disclosed in U.S. Pat. No. 5,586,874 to Hashimoto and U.S. Pat. No. 5,603,611 to Tarutani, allowing air to flow along a path from a high-pressure area to a low-pressure area. Thus, as the pressure in the air system downstream from the compressor lowers, airflow is directed from the cylinder channels to the air system through the valves provided at the outlet ports. Accordingly, air pressure above the pistons is lowered, thereby causing displacement of the swash plate and the pistons. As a result, the suction stroke generates a negative pressure sufficient to allow air to enter the cylinder block through the valves provided in the inlet port.
One disadvantage of these valve assemblies, however, is that they often provide check valves for only one direction of air flow, or are expensive to manufacture, or both. In order to operate at maximum efficiency, a piston compressor must provide a one-way valve both for air entering and for air exiting the cylinder channels. Such compressors require a compressor head assembly including multiple valves, some of which operate exclusively in a direction opposite to the direction in which some of the other valves exclusively operate. These arrangements are generally costly to manufacture. Additionally, such assemblies often prove to be somewhat difficult to assemble with the rest of the compressor.
What is desired, therefore, is an apparatus that provides inlet and outlet valves in a compressor that is inexpensive to manufacture. What is further desired an apparatus that provides inlet and outlet valves that is easy to assemble with the rest of a compressor.